Typically, residences, office buildings, apartment buildings and the like connect to a regional utility that provides power to buildings. This connection to the utility is generally through a meter that measures the amount of energy consumed by the connecting customer for billing purposes. However, recent trends have included adding to a typical utility power source on a premises by connecting renewable energy sources, standby power sources and/or electrical vehicles, among others, to reduce the amount of energy received from the utility and/or to compensate for a loss of power at the utility connection. For example, renewable energy sources, such as wind, solar and hydro-electric, may be generated on premises and may reduce the amount of power needed from the utility. Standby sources of power, such as fossil fuel motor-generators and battery-based sources, may be utilized as back-up energy sources when the utility power connection fails.
Additionally, many of these renewable or standby power sources may provide energy back to the utility that may then be provided to other customers of the utility. For example, electrical vehicles may function as a source of power to the premises as well as consume power, similar to battery-based storage. Also, energy generated by a wind, solar or hydro-electric source may be provided back to the utility and credited to offset the cost of the energy consumed on the premises.
FIGS. 1A, 1B and 1C illustrate typical existing utility power source installations before any additional alternative energy sources are added to the connection. The most common construction in the United States is currently represented by FIG. 1A. FIGS. 1B and 1C represent less common constructions that may still occur. Each system depicted in FIGS. 1A, 1B and 1C contains a meter socket and meter 1 connected to a load center 2. The load center 2 may include a main circuit breaker 3 and a plurality of branch circuit breakers 4 that provide the access points to the utility power. In FIG. 1A, the main circuit breaker 3 is located within the load center, while in FIG. 1B the main circuit breaker is located within the meter 1. In FIG. 1C, the meter and load center 2 are combined in what is referred to in the trade as a “meter-main-load center” or an “all-in-one” 5. Recent changes in the National Electric Code (NEC) require that no more than 20% of the panel rating in additional power sources be added, and that the addition is only permitted at the furthest point from the normal input. These changes thus limit the additional power sources to two sources.
FIG. 2 illustrates a prior art utility power source installation including several alternative energy sources connected to several of the plurality of branch circuit breakers 4. In the example, an alternative energy source 6 is connected to the premises electrical system through an external disconnect switch 7, which is typically required by the National Electric Code. Each switch 7 connects to the branch circuit breakers 4 in the load center 2 through a conductive line 9 and an over-current protective device 8, such as a fuse or circuit breaker. Thus, the alternative energy source 6 is connected to the load center 2 through the disconnect switch 7, the over-current protective device 8 and the conductive line 9. Shown in FIG. 2 are three separate alternative energy sources 6 connected to the branch circuit breakers 4 in this manner.
FIG. 3 shows another connection method that is known in the art. In some instances spaces in the branch circuit breaker 4 may not be available for use, such as if each of the plurality of branch circuit breakers are already connected or reserved. In this instance, the alternative energy source 6 may be connected at the line side of the main circuit breaker 3 using the disconnect switch 7, the over-current protective device 8 and the conductive line 9 discussed above with reference to FIG. 2. However, in this configuration, the utility power supply provided through the meter socket 1 would likely energize the circuit such that this connection configuration is not desired.
Several disadvantages exist for the prior art installation configurations discussed above. For example, the above connection configurations require a separate externally accessible disconnect switch 7 for each alternative energy device. Also, in typical load-centers 2, the circuit breakers 4 used for connection consume a space in the load center 2 that may be originally intended to be available for a premises load connection of a device. As a result, not enough spaces may exist in the load center 2 to connect all the devices. Another potential disadvantage of the prior art is that it may not provide information to a user regarding the amount of energy consumed or generated at a premises.
In addition, the prior art systems of connecting the alternative energy source to the utility connector is that it is “hard-wired” and thus has no ability to adapt to changing parameters such as utility rate schedules, cost of alternate fossil fuels, and possible utility premiums for consumption or generation of power at specific times. Also, the prior art connection systems cannot generally defer loads, such as an electric vehicle charging, until low demand hours to help relieve loading of the utility grid. While it would be possible to rewire a system to adapt to changing parameters, it would involve the use of an electrician, more hardware, and substantial costs to the customer.